Книга: Linux Network Administrator Guide, Second Edition

Defining mail transport protocols

Defining mail transport protocols

If you want sendmail to transport mail in any way other than by local delivery, you must tell it which transports to use. The MAILER macro makes this very easy. The current version of sendmail supports a variety of mail transport protocols; some of these are experimental, others are probably rarely used.

In our network we need the SMTP transport to send and receive mail among the hosts on our local area network, and the UUCP transport to send and receive mail from our smart host. To achieve this, we simply include both the smtp and uucp mail transports. The local mail transport is included by default, but may be defined for clarity, if you wish. If you are including both the smtp and the uucp mailers in your configuration, you must always be sure to define the smtp mailer first.

The more commonly used transports available to you using the MAILER macro are described in the following list:


This transport includes both the local delivery agent used to send mail into the mailbox of users on this machine and the prog mailer used to send messages to local programs. This transport is included by default.


This transport implements the Simple Mail Transport Protocol (SMTP), which is the most common means of transporting mail on the Internet. When you include this transport, four mailers are configured: smtp (basic SMTP), esmtp (Extended SMTP), smtp8 (8bit binary clean SMTP), and relay (specifically designed for gatewaying messages between hosts).


The uucp transport provides support for two mailers: uucp-old, which is the traditional UUCP, and uucp-new, which allows multiple recipients to be handled in one transfer.


This mailer allows you to send mail messages directly into Usenet style news networks. Any local message directed to an address of news.group.usenet will be fed into the news network for the news.group newsgroup.


If you have the HylaFAX software installed, this mailer will allow you to direct email to it so that you may build an email-fax gateway. This feature is experimental at the time of writing and more information may be obtained from http://www.vix.com/hylafax/.

There are others, such as the pop, procmail, mail11, phquery, and cyrus that are useful, but less common. If your curiosity is piqued, you can read about these in the sendmail book or the documentation supplied in the source package.

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